The disclosure relates generally to duct assemblies for transporting fluids such as exhaust gas from a combustion process and clean air to a combustion process. More particularly, the disclosure relates to duct assemblies that utilize a reduced amount of materials resulting in reduced material and construction costs.
Many industrial plants include furnaces, water heaters, and boilers that rely on combustion to generate heat, electricity, steam, or hot water, or to incinerate waste materials or residues. Duct assemblies are typically used to supply clean air to the combustion process and to transport dirty flue gas from the combustion process. Due to space limitations or other reasons, some duct assemblies can extend over relatively long distances (e.g., over 50 ft.). In addition, many duct assemblies are spaced above the ground so as not to interfere with plant operations and to enable easy access to the various equipment at the plant. Accordingly, many duct assemblies include rigid support structures for supporting the individual ducts above the ground. For example, referring now to FIGS. 1 and 2, a conventional duct assembly 10 is shown. Duct assembly 10 includes a lower duct 20 spaced above the ground 11, an upper duct 30 vertically spaced above lower duct 20, and a plurality of horizontally-spaced duct support stands 40 that support ducts 20, 30 above the ground 11. Stands 40 are spaced apart a distance D40. Ducts 20, 30 extend from stand 40 to stand 40, and thus, the portions of ducts 20, 30 spanning between each pair of adjacent stands 40 are not directly supported by stands 40.
Each duct 20, 30 includes an inner conduit 21, 31, respectively, and insulation 22, 32, respectively, that surrounds the entire perimeter of the corresponding inner conduit 21, 31. Each support stand 40 includes a pair of horizontally-spaced, vertical steel columns 41 and a plurality of transverse beams 42, 43, 44 extending horizontally between columns 41. In particular, lower transverse beam 42 is vertically disposed below both ducts 20, 30, intermediate transverse beam 43 is vertically disposed between ducts 20, 30, and upper transverse beam 44 is vertically disposed above ducts 20, 30. Transverse beams 42, 43, 44 provide structural integrity to stand 40 and maintain the relative spacing and positions of columns 41. In addition, lower transverse beam 42 directly supports lower duct 20, and intermediate transverse beam 43 directly supports upper duct 30. Accordingly, each beam 42, 43 must be sufficiently rigid and strong to support the weight of the corresponding duct 20, 30, respectively, and columns 41 must be sufficiently rigid and strong to support the weight of beams 42, 43, 44 and ducts 20, 30.